The present invention relates to a recording method and apparatus for an optical disk capable of writing data.
Conventionally, the CLV (Constant Linear Velocity) method is generally used for recording data on write once optical disks and erasable optical disks capable of recording data. Since the CLV method adopts a constant linear velocity for recording data on optical disks, basically the laser recording power is made constant. The write strategy, a technological method of controlling the laser recording power for accurate data recording for each disk, is fixed if the recording speed is unchanged.
When data is recorded on an optical disk, the data recording power of the laser beam needs to be adjusted because of differences in sensitivity, temperature, and recording environment such as an uneven dye thickness of the disk. Accordingly, the OPC (Optimum Power Control) is applied when data is recorded on a write once optical disk or an erasable optical disk. The OPC method adjusts the laser recording power for recording data on optical disks by irradiating laser beam to perform a test write of a specified pattern in the PCA (Power Calibration Area) of an optical disk.
The following describes an area configuration of CD-R, an example of write once optical disks. FIG. 11 shows a CD-R area configuration. As shown in FIG. 11, an optical disk 11 contains a lead-in area between diameters 46 mm and 50 mm. Outside this area, there are provided a program area and a lead-out area. The PCA is provided toward the inside of the lead-in area. The PCA comprises a test area and a count area. The program area can record digital audio data and computer-based data. The optical disk is 120 mm in diameter and allows recording up to the outside periphery of the lead-out area 118 mm in diameter.
The lead-in area records TOC (Table Of Contents) at the beginning of the optical disk. The TOC contains a list of track start positions. The lead-out area works as a buffer area following the last track on the disk to protect a disk player even if it attempts to read data over the last track. The PCA is a test write area for checking a laser's optimal write power and allows up to 99 test writes. A PMA is an area used for temporarily recording track information when data is written in track-at-once mode.
Before recording data, the OPC is performed to irradiate a laser beam to the PCA provided on the inside periphery of the lead-in area to effect a test write of specified pattern data. The OPC then proceeds to read the written data and finds an optimal power according to a given evaluation criterion, so that data can be actually recorded with the found optimal power.
The test OPC before the data recording is not sufficient for perfectly adjusting the recording power, because of laser wavelength changes and in-plane changes of the disk recording sensitivity during recording. As a solution, running OPC (also referred to as ROPC) is provided in addition to the test OPC. This technique monitors a recording signal waveform during the recording of data and calibrates the recording power so that the recording signal waveform becomes optimal. FIG. 12 shows waveforms corresponding to a recording signal of laser beam for recording and a light signal of the reflected light, and pits formed on an optical disk to record data. When the recording signal is applied as a pulse signal at a specified time interval as shown in FIG. 12, the light signal of the reflected light becomes a peak value HS at the beginning of irradiating the laser beam for recording. When the laser beam just starts being irradiated to the optical disk, no pits are formed on the optical disk and the irradiated light is reflected entirely. After the peak value HS, the amount of reflected light gradually decreases as the pit is formed. The light signal level of the reflected light almost becomes a stable value HL. When the recording signal rises, the light signal of the reflected light also rises.
The above-mentioned waveform characteristics result from the light signal of the reflected light of the laser beam irradiated to the optical disk. Conventionally, the running OPC is performed to control the recording laser beam power by monitoring the light signal waveform so as to constantly stabilize the light receiving signal level, thereby controlling the value HL almost in flat or stable level.
In recent years, an increase of personal computer capacity and user needs accelerates recording speeds (linear velocity scales) of write once optical disks and erasable optical disks. At present, the linear velocity scales according to the CLV method are 16 times for write once optical disks and 10 times for erasable optical disks. The CLV method requires a higher rotational speed on an inner periphery of the optical disk. When the CLV method is used to record data at the linear velocity scale of 12 times, for example, the outermost periphery shows a disk rotational speed of 2400 rpm while the innermost periphery shows a disk rotational speed of approximately 6000 rpm. When the linear velocity scale is set to 16 times, the innermost periphery shows a disk rotational speed of approximately 8000 rpm.
When the CLV method is used to record data on the inside periphery of the optical disk, the disk is subject to a very high rotational speed, causing self vibration to the disk. In such a case, the beam spot size changes in a recording section even if data is recorded on the optical disk with the constant laser recording power. The recorded data may not be read correctly. The disk may be damaged if it is subject to excessive rotational vibration.
When the test OPC or the running OPC is performed with the optical disk vibrated, an inappropriate value is obtained for the optimal power value as the reference for the data recording power. This may create a deficient disk where no data can be read.
Japanese Patent No. 3225704 discloses the technology concerning the optical disk recording method and apparatus for maintaining an appropriate recording state in response to changing conditions during recording on an optical disk. The invention disclosed in this patent forms a pit by irradiating the recording laser beam to the optical disk to write data in terms of the length of the pit. For this purpose, the recording power of the recording laser beam is variably controlled on the basis of a recording power value for the recording laser beam irradiated to the optical disk, and a stable value or its equivalent of the reflected light power in a state where the reflected light power of recording laser beam passes a peak value at the beginning of irradiation and becomes almost stable.
The above-mentioned invention detects, the during data recording, a recording power value HS for recording laser beam irradiated to the optical disk; and a stable value or its equivalent HL for the reflected light power in a state where the reflected light power of recording laser beam passes a peak value at the beginning of irradiation and becomes almost stable, and finds ratio HL/HS. A recording power value of the irradiated laser beam is variably controlled so that the ratio becomes a predetermined optimal value based on an experiment or the like. Since the recording power is appropriately controlled at each time point, an optimal recording state is stably obtained.
The above-mentioned problem can be solved by keeping a low rotational speed on the inside periphery when data is recorded on the optical disk. The CAV (Constant Angular Velocity) method does this. The CAV method provides an almost constant rotational speed (angular speed) and causes a lower linear velocity on the inside periphery compared to the outside periphery. For example, the CAV method enables the linear velocity scale of 30 times on the outermost periphery and 12 times on the innermost periphery. This method changes the linear velocity scale depending on a radial position of the recording laser beam irradiated on the optical disk in the radial direction. Since the CAV method always keeps the number of disk rotations constant, however, it can provide stable writing by suppressing a rotational speed on the inside periphery.
Since the CAV method increases the linear velocity scale toward the outermost periphery of the optical disk as mentioned above, the recording laser beam power needs to be changed according to positions on the optical disk in the radial direction. When the running OPC is performed, the optimal power value obtained by the test OPC can be only applicable to some areas on the inside periphery of the optical disk.
Since the above-mentioned Japanese Patent No. 3225704 shows no reference to changes of the linear velocity scale, it is supposed to disclose the technology according to the CLV method. Accordingly, the technology disclosed in this patent cannot be applied to the CAV method.
Conventionally, the CAV method does not perform the running OPC, because there has not been available an appropriate control method of changing an optimal power value dependently on the linear velocity scale.